In a great number of technological fields, rotatable assemblies are used wherein components of such assemblies rotate, during operation, at very high speeds, mostly supported by a driving shaft which is driven into rotation. Similarly, in most instances, the shaft itself is supported by bearings. Theoretically speaking, the center of mass of such assemblies should, as accurately as possible, coincide with, or lie in, the axis of rotation. In practice, this is hardly ever the case with the accuracy which would be desirable, because of manufacturing tolerances and lack of homogeneity of the material of the components, as the two main causes for inaccuracy. It is well known that the condition thus described and referred to as mass unbalance is most undesirable.
One of the various consequences of mass unbalance is the detrimental effect upon the bearings which are known to wear out rapidly under these conditions. Also, it is undesirable to transmit unbalance forces or moments to the structure supporting the rotating assembly. Moreover, in many fields of application, mass unbalance is undesirable for other reasons, such as the inaccuracies which may thereby be introduced into the operation of a measuring or indicating instrument. As one example to be mentioned, such field of application is in connection with gyroscopes wherein it is well known that means should be provided which permit eliminating mass unbalance as much as possible.